Investigations were carried out on the gill tissues of African cat fish (Clarias gariepinus) exposed to sub lethal concentrations (0.002, 0.003, 0.004, 0.005 and 0.006 mgl^‑1) of soap and detergent effluents in a static renewal bioassay procedure for a total period of 52 days. The histopathological studies of the sectioned gills of this fish species showed marked histological alterations. The observed pathological lesions of the gills include infiltration of secondary lamellae, inter-lamellae hyper plastic lesion, oedema (an indication of ballooning dilatation in form of club deformation at the tip of secondary lamellae), congestion of the blood vessels, epithelial thickening and lifting, and necrosis of various degrees. The degree of all these recorded anomalies is concentration dependent. All the fishes held in the control stock showed inappreciable or no histological degradation as a result of stress in the course of handling while their staining patterns and cellular arrangement remained unaffected. Therefore, indiscriminate human exposure to such concentrations of this effluent is dangerous to health.

Key words: Clarias geriepinus, histological, sub lethal, soap and detergent, effluent and pathological.

ub lethal, soap and detergent, effluent and pathological.